1. Field of the invention
The present invention relates to an ink jet recording apparatus. More particularly, the invention concerns an electro-mechanical transducer employed in the ink jet recording apparatus.
2. Background of the invention
Conventionally, an electro-mechanical transducer having piezo-electric members is employed in an ink jet recording device. The piezo-electric member vibrates in different vibrating modes depending upon its shape, the direction that the member is polarized, or the direction that an electronic field applied thereto. For example, where the piezo-electric member is in the form of plate which is rectangular in cross-section and is polarized in a direction along its transverse direction, applying an electronic field along its polarized direction makes the piezo-electric member contract along its longitudinal direction and expand along its transverse direction, while applying an electronic field to the piezo-electric member reverse to the polarized direction makes the piezo-electric member expand along its longitudinal direction and contract along its transverse direction. A vibration along the longitudinal direction will be referred to as "a d(31) mode" while a vibration mode along the transverse direction will be referred to as "a d(33) mode". Further, applying the electronic field to the piezo-electric member perpendicular to its polarized direction introduces therein a shear stress along its surface. This vibration mode is referred to as "a d(15) mode" hereinafter.
Each prior art electro-mechanical transducer employs one of these vibration modes, the d(33) or d(31) mode being mainly employed among them. Further, a prior art ink jet recording device includes the electro-mechanical transducer. Each transducer has therein an ink chamber in which an elongated piezo-electric member is arranged. The piezo-electric member is vibrated according to image signals. Then, in response to displacements of the piezo-electric member and the resultant energy generated in the ink, ink droplets are ejected from the ink chamber through a nozzle formed in a wall of the chamber.
For instance, U.S. Pat. No. 4,752,788 discloses an ink jet head which is shown in FIG. 1. This ink jet head 10 includes a piezo-electric member 11 in which a plurality of parallel slots 12 are formed, and a plate 13 for covering the slots 12 to define respective ink chambers 14. Each slot 12 has at its bottom portion a pair of slits extending in a longitudinal direction thereof so as to define therebetween an elongated mount 15. An electrode 16 is arranged on the upper surface of the mount 15, and another electrode 17 is provided on a lower surface of the piezo-electric member 11 opposing electrode 16. In operation of the head 10 thus constructed, applying a voltage between the electrodes 16 and 17 causes the mount 15 to deform, which varies a volume of the ink chamber 14. This energizes ink in the chamber 14 so that a droplet of the ink is ejected through a nozzle which is not shown.
Further, Japanese Patent Laid-Open Publication No. 6-143563 discloses another ink jet head 20 depicted in FIG. 2. The head 20 has a first base plate 21. The plate 21 includes a plurality of parallel slots 22 which are covered by a compliant film 23 to define a plurality of corresponding ink chambers 24. The head 20 also has a second base plate 25. This plate 25 has thereon a plurality of mutually spaced piezo-electric vibrators 26 for drive as well as a dummy piezo-electric vibrator 27. These piezo-electric vibrators 26 and 27 are constructed by superimposing piezo-electric thin layers and electrode layers alternately. The second base plate 25 is arranged on the first base plate 21 so that each vibrator 26 contacts with the compliant film 23 over the ink chamber 24. The drive and dummy vibrators 26 and 27 are typically formed by first bonding a layered piezo-electric plate on the plate 25 and second forming grooves in the plate at equal intervals. The first base plate 21, compliant film 23, and the second base plate 25, including the vibrators 26 and 27, are held securely by rigid plates 28 and 29 using bolts. In operation of the ink jet head 20 thus constructed, applying voltage on the vibrator 26 causes it to deform, which moves the complaint film 23 to force the ink so that the volume of the ink chamber 24 varies and then an ink droplet is ejected through a nozzle which is not shown.
However these prior arts ink jet heads employs one of d(31), d(33), or d(15) vibration modes, each of which provides for only a small deformation with the piezo-electric member. Therefore, the ink is not sufficiently energized in response to the image signals.
Further, in the above mentioned systems, the vibration of one piezo-electric member is transmitted to the neighboring ink chambers and piezo-electric members, i.e., a cross-talk from chamber to chamber is occurred, which results in unexpected ink ejections from those ink chambers so that the resultant image of a recording device is damaged.